The processing of photographic silver halide color films generally involves the steps of color development, bleaching, fixing, stabilizing and drying. The stabilizing bath is generally used as the final chemical processing step in order to reduce stain and/or to enhance dye stability, as well as to wash off the last residues of processing chemicals from previous steps. Dye stability is believed to be affected by the presence of unreacted dye forming coupler in the silver halide emulsion layers of the film, which coupler can then react to degrade the color image. Dye stability is also influenced by temperature, humidity, air quality and exposure to light. In certain instances, the magenta dye forming coupler tends to fade more rapidly than other dye forming couplers, and a stabilizing formulation often includes a compound that releases a methylene group to inhibit magenta dye fade. Stabilizing solutions are aqueous formulations containing the various components necessary to provide dye stability as well as to reduce scumming and chemical residues on the film. In some instances, the stabilizing formulation may be in the form of a solid that is dissolved in water in the processing bath.
Typical known stabilizing solutions often contain formalin (or a formaldehyde precursor) or another aldehyde, as the methylene-releasing compound. See for example, U.S. Pat. No. 5,273,864 (Ishikawa et al). Formaldehyde possesses the added benefit of high volatility, so that any residual formaldehyde on the base side of the film is readily removed in the drying step. However, in recent years, concerns over the hazardous effects of formaldehyde have stimulated the development of alternative stabilizing compounds. Hence, alternative aldehydes have been used, as described in U.S. Pat. No. 5,362,609 (Kuwae et al).
Hexamethylenetetramine (HMTA) is an acceptable substitute for some or all of the formaldehyde in the stabilizing solutions. As described in U.S. Pat. No. 5,529,890 (McGuckin et al), HMTA is a water-soluble, nonvolatile, crystalline compound with superior methylene group-releasing properties. However, sometimes this compound leaves residue on the dried films, so there have been efforts to reduce this effect by adding certain surfactants to the stabilizing solution. A particularly useful combination of an anionic sulfate or sulfonate and a nonionic polyethoxylated surfactant is described in the noted McGuckin et al patent.
It is also known to include in stabilizing solutions one or more metal ion sequestering agents and alcoholamines, such as diethanolamine, as described in U.S. Pat. No. 4,927,746 (Schwartz). The alcoholamines are considered useful to reduce sulfurization (or sulfur precipitation) resulting from the carryover of a thiosulfate fixing agent into the stabilizing bath. Sulfurization is a serious problem resulting in fouling of processing equipment and the processed film. An "alkanolamine" refers to a compound in which the nitrogen atom is directly attached to a hydroxyalkyl group, examples of which are defined hereinbelow.
Still further, it is known to include one or more biocides in stabilizing solutions in order to retard biological growth. Various biocides are known including various isothiazolones such as 1,2-benzisothiazolin-3-one commercially available under the trademark PROXEL.TM. GXL from Zeneca, and the mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one found in a product commercially available from Rohm and Haas under the trademark KATHON.TM. LX.
One commercially available stabilizing solution useful for processing silver halide color negative films includes HMTA, diethanolamine, a mixture of surfactants, a sequestering agent and a PROXEL.TM. GXL biocide. It was found that under certain conditions and in certain processing machines, biocidal effectiveness was reduced for some reason and biogrowth would appear. Obviously, there is a need to provide a more effective biocidal effect in such solutions. An effort was made to replace the PROXEL.TM. GXL biocide with the KATHON.TM. LX biocide in stabilizing solution concentrates because it was expected that the isothiazolone compounds would be interchangeable. However, we observed that problems arose with this substitution. Specifically, the KATHON.TM. LX biocide was not stable in the presence of HMTA and an alkanolamine, and rapidly lost its effectiveness.
There is a need for a means to provide a formaldehyde-free chemical concentrate(s) for providing a photographic stabilizing solution that inhibits biogrowth while providing image dye stability.